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Complexation and Redox Buffering of Iron(ll) by Dissolved Organic Matter

机译：溶解的有机物对铁（II）的络合和氧化还原缓冲作用

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摘要

Iron (Fe) bioavailability depends upon its solubility and oxidation state, which are strongly influenced by complexation with natural organic matter (NOM). Despite observations of Fe(II)-NOM associations under conditions favorable for Fe oxidation, the molecular mechanisms by which NOM influences Fe(Ⅱ) oxidation remain poorly understood. In this study, we used X-ray absorption spectroscopy to determine the coordination environment of Fe(Ⅱ) associated with NOM (as-received and chemically reduced) at pH 7, and investigated the effect of NOM complexation on Fe(Ⅱ) redox stability. Linear combination fitting of extended X-ray absorption fine structure (EXAFS) data using reference organic ligands demonstrated that Fe(Ⅱ) was complexed primarily by carboxyl functional groups in reduced NOM. Functional groups more likely to preserve Fe(Ⅱ) represent much smaller fractions of NOM-bound Fe(Ⅱ). Fe(Ⅱ) added to anoxic solutions of as-received NOM oxidized to Fe(Ⅲ) and remained organically complexed. Iron oxidation experiments revealed that the presence of reduced NOM limited Fe(Ⅱ) oxidation, with over 50% of initial Fe(Ⅱ) remaining after 4 h. These results suggest reduced NOM may preserve Fe(Ⅱ) by functioning both as redox buffer and complexant, which may help explain the presence of Fe(Ⅱ) in oxic circumneutral waters.
机译：铁（Fe）的生物利用度取决于它的溶解度和氧化态，这与天然有机物（NOM）的络合强烈影响。尽管在有利于铁氧化的条件下观察到Fe（II）-NOM的缔合，但对NOM影响Fe（Ⅱ）氧化的分子机理仍知之甚少。在这项研究中，我们使用X射线吸收光谱法确定了pH值为7时，Fe（Ⅱ）与NOM（按原样还原并化学还原）相关的配位环境，并研究了NOM络合对Fe（Ⅱ）氧化还原稳定性的影响。 。使用参考有机配体对扩展的X射线吸收精细结构（EXAFS）数据进行线性组合拟合表明，Fe（Ⅱ）主要由还原型NOM中的羧基官能团络合。更有可能保留Fe（Ⅱ）的官能团代表NOM结合的Fe（Ⅱ）的比例要小得多。 Fe（Ⅱ）加入到原样NOM氧化为Fe（Ⅲ）的缺氧溶液中并保持有机络合状态。铁氧化实验表明，还原型NOM的存在限制了Fe（Ⅱ）的氧化，在4 h后剩余了50％以上的初始Fe（Ⅱ）。这些结果表明，减少的NOM可以通过充当氧化还原缓冲剂和络合物而保留Fe（Ⅱ），这可能有助于解释在有氧环境中性水中Fe（Ⅱ）的存在。

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  • 来源
    《Environmental Science & Technology》 |2017年第19期|11096-11104|共9页
  • 作者

    Ellen E. Daugherty; Benjamin Gilbert; Peter S. Nico; Thomas Borch;

  • 作者单位

    Department of Chemistry, Colorado State University, 1170 Campus Delivery, Fort Collins, Colorado 80523, United States;

    Energy Geoscience Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States;

    Energy Geoscience Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States;

    Department of Chemistry, Colorado State University, 1170 Campus Delivery, Fort Collins, Colorado 80523, United States,Department of Soil and Crop Sciences, 1170 Campus Delivery, Fort Collins, Colorado 80523, United States;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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